This invention pertains to a method of disposing of certain non-biologic organic waste material in an environmentally acceptable manner. More particularly, it pertains to a method of converting such material to a substantially impermeable, load-bearing construction material.
Society's increasing concern with the environmentally safe disposal of industrial wastes has led to the development of a variety of processes in which said wastes are incorporated in, or encapsulated in, a cementitious material. Upon hardening, such material is suitable for use as a construction or landfill material.
The adaptability of such processes to the disposal of a wide variety of waste materials, including organic waste materials, is suggested, for example, in British Pat. No. 1,485,625--Chappell and U.S. Pat. Nos. 3,947,284--Kitsugi et al, 3,980,558--Thompson, and 4,209,335--Katayama et al. The teachings of these references are directed primarily to the utilization of Portland cement as the encapsulation material. The terms used however are not necessarily consistent. The British Chappell patent, for example, describes the cement as: "calcium-containing cements . . . for example, those complying with British Standards 12 (1958), 4027 (1966), 4248 (1968), 146 (1968), 4246 (1968), 1370 (1958) or 915 (1947)" (Page 2, Column 2, lines 66-70), combined with an aluminosilicate, typically fly ash.
Waste incorporatable in this matrix according to Chappell are said to include "paint wastes," "printing and duplicating wastes," "explosives industry wastes excluding organic wastes produced by this industry," "Latex wastes and cyanide, mercury and zinc wastes produced by the rubber and plastics industry," "textile wastes," "pulp and paper industry wastes," "leather industry wastes," and "sewage sludges" (Page 2, Column 2, lines 5-56). The examples in the Chappell patent refer to an oily waste comprising 2 percent mineral oil and 94 percent water (Example 8), a latex waste produced by the upholstery industry and comprised of 12 percent organic, 1 percent inorganic, and 87 percent water (Example 11), and digested sewage sludge (Example 14). Portland cement is used in each of these examples.
Kitsugi et al teaches that certain waste sludges may be rendered amenable for incorporation in a Portland cement mix by the further inclusion of an alkali or calcium sulfate compound. The waste thus treated is one having a high water to solid ratio and containing a substance having "a harmful effect on the setting of normal portland cement . . . , for example an organic substance . . . sugar, a cracked petroleum substance, a fat and a humic substance . . . and an organic phosphorus compound such as parathion" (Column 1, lines 7-35).
Katayama et al also discloses that waste sludges, referred to there as "Hedro," may be disposed of by a mixture with hydraulic cement. The Katayama et al patent indicates the cement used is preferably "portland cement, but it is as well possible to use portland blast-furnace cement, silica cement, fly ash cement, pozzolan cement, etc." (Column 2, line 68 to Column 3, line 3). The Hedro is said often to include substances which hamper or inhibit hydraulic cement from hardening, such as "saccharides, humins, tannins, fats and fatty oils, humuses, [etc.]" (Column 1, lines 44-48). Katayama refers to a so-called synergistic effects resulting from the use of an additive to permit the hydraulic cement to set up even in the presence of these harmful or cement inhibiting compounds. The additives consist generally of a sulfate, together with a carbonate, bicarbonate, or silicate, and may further include a hydroxide or oxide of an alkali earth metal (Column 3, lines 3-24).
Katayama's Example 1 pertains to solidifying, with Portland cement, the effluent sludge of a food processing plant containing considerable organic matter [which is said to hamper hydraulic cement from hardening by hydration], such as saccharides or the like (Column 1, lines 45-48). The sludge was comprised of 91% water and exhibited a weight reduction upon heating, for 30 minutes at 800.degree. C., of 70 percent. Use of the cement in a proportion of up to 30 percent, without the additive, failed to produce a hardenable mixture. The addition of 10 percent calcium hydroxide, however, resulted in hardening of the mixture and this enhancement was even greater with the further addition of aluminum sulfate and sodium carbonate, along with some reduction of the calcium hydroxide.
A fly ash cement, presumably Portland cement combined with fly ash, is utilized in Example 5, without the additives, and is demonstrated apparently to produce an unsatisfactory hardening in combination with a waste consisting of electrostatic precipitator dust from a community incinerator. PCB-contaminated Hedro (1,000 PPM PCB) is solidified, according to Example 7, utilizing Portland cement. The remaining examples are similar, that is, Portland cement is used in each case in which the waste includes any organic material, even as a contaminent.
Thompson similarly discloses a process for disposing of liquid or semi-liquid wastes containing soluble toxic material by admixing the waste with a solidifying agent consisting essentially of a hydraulic cement in an amount sufficient to provide a fluid mass which will set upon standing to a contiguous rock-like solid consistency. According to the Thompson patent, it has been unexpectedly found that the liquid or semi-liquid wastes must be admixed with the hydraulic cement in an amount of at least 9 pounds hydraulic cement per gallon of waste containing from about 30 to about 40 volume percent solids to provide an admixture which will be sufficiently fluid yet will set to a contiguous rock-like solid consistency of sufficient strength and non-porosity to entrap the soluble toxic materials in the waste to prevent leaching (Column 2, lines 68 to Column 3, line 7). Even then, the mixture is preferably poured into a subsurface soil pit lined with a moisture impervious film prior to setting and is subsequently covered with a layer of soil. While the process is said to be particularly useful in disposing of liquid sludge waste from chemical processes for the manufacture of phosphoric acids, particularly aqueous filter aid sludges (and it is this specific sludge which is addressed in each of the examples), the Thompson patent otherwise suggests that the process is useful with "substantially any type of liquid or semi-liquid waste containing soluble toxic materials" (Column 4, lines 53 and 54). Moreover, the "hydraulic cement" useful in this process is said to "include all mixtures of lime, silica and alumina, or of lime and magnesia; silica, alumina, and iron oxide and other like mixtures of ingredients which set upon the action of water to a contiguous rock-like solid consistency [including] hydraulic limes, grappier cement, puzzolan cements, and Portland cements" (Column 3, lines 52-59).
While the foregoing references seem to suggest that the applicability of their teachings extend to disposal processes and compositions involving cementitious material other than Portland cement, these suggestions are tenuous at best. The extension of these teachings to a cementitious material or system comprised of lime and fly ash is even more speculative, particularly in the context of a waste or disposal of a waste with known cement-inhibiting characteristics such as one which is predominantly organic in character.
In contrast to the cementitious reaction of Portland cement, in which lime or calcium hydroxide is produced, fly ash (primarily the collected stack dust from a pulverized coal burning combustion unit) is a pozzolan which forms cementitious products through the consumption of lime. Moreover, the speed of reaction in these systems is quite different. Portland cement sets to approximately 50 percent of its strength within 24 hours. In contrast, significant strength and impermeability is not generally developed in a lime-fly ash system before about 7 days and 50 percent of ultimate strength is generally not achieved until about 30 days. These characteristic features are believed to be only the more readily discernable indications of the significantly different chemistry in a lime-fly ash cementitious system as compared with a Portland cement system.
Because of the ready availability of fly ash as a waste material (it is considered by some to be an environmental hazard in itself), fly ash is a highly practical constituent for disposal processes, by which other wastes may be incorporated in an environmentally acceptable cementitious matrix. And indeed that factor had led to the fairly widespread use of lime-fly ash disposal processes as exemplified, for example, by the POZ-O-TEC.RTM. process commercialized by Conversion Systems Inc., the assignee of the present invention, for the disposal of sulfite-containing flue gas desulfurization sludges. Lime-fly ash cementitious compositions have also been found useful for the disposal of characteristically inorganic industrial waste sludges, particularly those including sulfate compounds (as disclosed and claimed in U.S. Pat. No. Re. 29,783--Smith et al), for coal mining refuse (as disclosed and claimed in U.S. Pat. No. 3,870,535--Minnick et al), and for digested sewage sludge (as disclosed in U.S. Pat. No. 4,028,130--Webster et al), all of common assignment herewith.
Of further background interest is U.S. Pat. No. 3,206,319--Minnick et al which discloses a road base composition comprised substantially of aggregate and incorporating a cementitious matrix comprised of lime-fly ash and bitumen. In general "bitumen," which is self-setting, is emulsified asphalt or an asphalt from which petroleum distillate-soluble components have been removed.
Further, it is known that in certain commercial operations preceding the present invention, small amounts of organic materials (primarily oils and greases) have been included in limited amounts (on the order of 2-5 percent) in other industrial waste, which has been treated and disposed of by the incorporation of the waste in a lime-fly ash cementitious matrix.
Notwithstanding this background, there remains a pressing need for a process for the disposal of a wide variety of non-biologic, organic wastes in an economic and environmentally acceptable manner. As used herein, the term "organic waste," unless otherwise indicated, refers to a physically unstable (i.e., nonload-bearing and penetrable) by-product of a commercial process, the chemical constituents of which, other than water, are predominantly, or at least characteristically, organic in nature. "Non-biologic" indicates that the organic character of the waste is due to the inclusion of organic compounds other than proteins, carbohydrates, and like compounds typically of direct biologic origin.
Disposal of such wastes in a lime-fly ash cementitious matrix has not heretofore been considered acceptable. This is thought to be due to the widespread understanding that organic materials generally inhibit or interfere with cementitious reactions and may be tolerated in substantial amounts in such reactions only within specific limitations as to reaction-enhancing additives, amounts, or characteristic types of organics, (e.g., digested sewage sludge).
This understanding is further evidenced by express regulatory directives which indicate, for example, "[lime-fly ash] techniques are generally better suited for stabilizing inorganic wastes rather than organic wastes. The decomposition of organic material in the sludge mass after curing can result in increased permeability along with some decrease in the strength of the material." Among the disadvantages of such techniques are listed "stabilized sludges are vulnerable to acidic solutions and to curing and setting problems associated with inorganic (sic) contaminants in the waste sludge (Page 16, Toxic and Hazardous Waste Disposal, Vol. 1, "Processes for Stabilization/Solidification," edited by Robert B. Pojasek, Ann Arbor Science Publishers, Inc., 1979). On Page 21 of the same text in Table 2 under the fixation system identified as "lime-based" (otherwise identified to comprise lime-fly ash systems), the column entitled "Materials to Which System is Not Applied" lists "organic wastes, toxic anions."
It is, therefore, the general object of the present invention to provide a method of disposing of at least certain types of organic waste materials by the incorporation thereof, in substantial amounts, in a practical and economical cementitious matrix material.
A further object of this invention is to provide a method for converting selected physically unstable organic wastes to a load-bearing and substantially impermeable construction material of reduced leachability and thus to permit use or disposal of the waste in a practical and environmentally acceptable manner.